1. Field of Invention
The invention relates to a liquid crystal display (LCD) device and, in particular, to a pixel arrangement and a driving method of an LCD device.
2. Related Art
An LCD device is one type of usually flat panel displays and has the advantages of high resolution, light weight, a thin thickness, and low power consumption. Thus, LCD devices, which are more and more widely, used serve as computer display devices and touch screens for man-machine interfaces, and are also combined with video systems to form televisions.
However, the LCD device still has some technological problems to be solved, such as the problem of wide angle viewing. The viewing angle of the LCD device relates to the γ property thereof. The γ property represents the relationship between the gray-scale value and the luminance of the image. FIG. 1 shows characteristic curves of gray-scale values versus light transmittances in a multi-domain vertical alignment mode LCD panel according to the prior art. As depicted in FIG. 1, curves L1 to L3 represent the light transmittances observed from a front side of the multi-domain vertical alignment mode LCD panel. The curve L1 represents the red light transmittance, the curve L2 represents the green light transmittance, and the curve L3 represents the blue light transmittance. However, when viewing the multi-domain vertical alignment mode LCD panel at the tilt angle of 60 degrees, the observed light transmittance changes according to the same operation voltage so that the curves L1, L2, L3 respectively drift to the curves L4, L5, L6.
As depicted in FIG. 1 again, the light transmittance of the curve L1 approaches the light transmittance of the curve L4, the light transmittance of the curve L2 approaches the light transmittance of the curve L5, and the light transmittance of the curve L3 approaches the light transmittance of the curve L6 in the areas with the higher gray-scale value and the lower gray-scale value. However, the light transmittances of the curves L1, L2 and L3 are separated from those of the corresponding curves L4, L5 and L6 in the middle gray-scale area. That is, the color shift phenomena in the higher gray-scale area and the lower gray-scale area is slight, and the color shift phenomenon in the middle gray-scale area is more pronounced.
FIG. 2 is a graph depicting the relationship between normalized luminances of the images viewed in front of and in neighboring the front of the screen using the same gray-scale value in the conventional LCD device, wherein the dashed line represents the ideal values, and the solid line represents the actual values. More specifically, the γ properties of the images viewed in front of, and neighboring the front of the screen under the ideal condition are the same. Therefore, the relationship between the normalized luminances appears as a straight line with the slope of 1, as depicted by the dashed line of FIG. 1. In practice, however, the LCD device has the problem that the viewing angle is not wide enough. Thus, when the user is watching the image in front of and neighboring the front of the screen, they properties of the viewed images are different. That is, the normalized luminances of the images viewed by the user in front of and neighboring the front of the screen are different. Usually, the normalized luminance of the image viewed in front of the screen is higher than the normalized luminance of the image viewed from a position neighboring the front of the screen. Thus, the luminance difference between the frames viewed at different angles on the multi-domain liquid crystal screen causes the different results of the color mixing, and the apparent colors still have some difference so that the color shift phenomenon is produced.
To solve the above-mentioned problems, the prior art changes the circuit layout and addresses the color shift phenomenon based upon the data of FIG. 1 that suggests the color light with the higher gray-scale value and the lower gray-scale value may have the slighter color shift phenomenon. In this prior art, a pixel unit is divided into two areas with different light transmittances. One of the areas has the light transmittance and displays the higher gray-scale color, and the other area has lower light transmittance and displays the lower gray-scale color. More particularly, the user may see a similar color when watching the improved multi-domain vertical alignment mode LCD panel with a middle gray-scale color, which is formed by mixing the higher gray-scale color with the lower gray-scale color, whether viewed straightened or slanted.
Referring to FIG. 3, a conventional multi-domain LCD device 1 includes a liquid crystal panel 100, a source driver 102 and a gate driver 104. The liquid crystal panel 100 includes n×m pixels 10. The source driver 102 transfers display data to the pixels 10 through data lines D(1) to D(n), respectively. The gate driver 104 transfers scan signals to the liquid crystal panel 100 through scan lines S(1) to S(m) to sequentially turn on each column of pixels 10, and transfers a first bias signal and a second bias signal to each pixel 10 on the liquid crystal panel 100 through first storage capacitor lines B1(1) to B1(m) and second storage capacitor lines B2(1) to B2(m), respectively. As depicted in FIGS. 4 and 5, a pixel divided structure of the LCD device 1 proposed in the prior art has a plurality of pixels 10 arranged in a matrix. Each pixel 10 includes a first sub-pixel 11 and a second sub-pixel 12. Each first sub-pixel 11 includes a liquid crystal capacitor CLC1, a storage capacitor CST1 and a switch element M1, and each second sub-pixel 12 includes a liquid crystal capacitor CLC2, a storage capacitor CST2 and a switch element M2. In addition, the LCD device 1 further includes a plurality of scan lines S(1) to S(m), a plurality of data lines D(1) to D(n) and a plurality of storage capacitor lines 15. The storage capacitor lines 15 include the first storage capacitor lines B1(1) to B1(m) and the second storage capacitor lines B2(1) to B2(m). The scan lines S(1) to S(m) and the storage capacitor lines 15 are disposed in parallel and alternately, and the data lines D(1) to D(n) are perpendicular to the scan lines S(1) to S(m). As depicted in FIG. 4 and taking one of the pixels 10 as an example, the ith scan line S(i) is disposed between the first sub-pixel 11 and the second sub-pixel 12 and connected to the gates of the switch element M1 and the switch element M2, and the jth data line DO) is connected to the liquid crystal capacitor CLC1 and the storage capacitor CST1 through the switch element M1, and connected to the liquid crystal capacitor CLC2 and the storage capacitor CST2 through the switch element M2. In addition, the storage capacitor CST1 and the storage capacitor CST2 are respectively connected to the ith first storage capacitor line B1(i) and the ith second storage capacitor line B2(i), wherein the ith second storage capacitor line B2(i) and the (i+1)th first storage capacitor line B1(i+1) share the same physical circuit layout.
FIG. 5 is a schematic illustration depicting the circuit layout of several pixels 10, wherein the area A represents the display area of the first sub-pixel 11, the area B represents the display area of the second sub-pixel 12, and the areas A and B are alternately disposed along the scan line direction alternately. Herein, a dot inversion polarity switching method is provided as an example, in which the pixel voltages of the same pixel in neighboring frame times have different polarities, and the pixel voltages of the neighboring pixels also have different polarities. When one of the pixels 10 is enabled, its operation timing is depicted in FIG. 6. Taking the area A as an example, the ith first storage capacitor line B1(i) turns to the low voltage level after the ith scan line S(i) outputs the scan signal in a first frame time f1. Thus, the pixel voltage (i.e., the capacitance of the liquid crystal capacitor CLC1) in the area A is influenced by the storage capacitor CST1 and is slightly decreased from the original “X” to “X−ΔV”. In a second frame time f2, the ith first storage capacitor line B1(i) again turns back to the high voltage level after the ith scan line S(i) outputs the next scan signal. At this time, the pixel voltage (i.e., the capacitance of the liquid crystal capacitor CLC1) in the area A is influenced by the storage capacitor CST1, and is slightly increased from the original “−X” to “−X+ΔV”. In addition, taking the area B as an example, the ith second storage capacitor line B2(i) turns to the high voltage level after the ith scan line S(i) has outputted the scan signal and one half clock is elapsed in the first frame time f1. Thus, the pixel voltage (i.e., the capacitance of the liquid crystal capacitor CLC2) in the area B is influenced by the storage capacitor CST2 and is slightly increased from the original “X” to “X+ΔV”. In the second frame time f2, the ith second storage capacitor line B2(i) turns back to the low voltage level after the ith scan line S(i) has outputted the next pulse signal and one half clock has elapsed. At this time, the pixel voltage (i.e., the capacitance of the liquid crystal capacitor CLC2) in the area B is influenced by the storage capacitor CST2, and is slightly decreased from the original “−X” to “−X−ΔV”.
As mentioned above, the same pixel is further divided into two sub-pixels in the prior art, and the γ property of the LCD device 1 is improved by controlling the pixel voltages of the two sub-pixels, as depicted in FIG. 7. As depicted in FIG. 5, however, this method makes the pixel voltage difference of the first sub-pixel 11 become “X−ΔV” (in the first frame time f1) or “−X+ΔV” (in the second frame time f2) to generate a lower gray-scale color, for example, and makes the pixel voltage difference of the second sub-pixel 12 become “X+ΔV” (in the first frame time f1) or “−X−ΔV” (in the second frame time f2) to generate a higher gray-scale color, for example. As mentioned hereinabove, when the higher gray-scale color and the lower gray-scale color are mixed to form a middle gray-scale color, the color shift phenomenon can be improved.
FIG. 8 is a graph depicting the relationship between the transmittance and an input voltage in a conventional LCD device. When an input voltage X is in the low transmittance representation, the fixed ΔV makes the luminance of the bright zone be different from that of the dark zone. However, this phenomenon can be corrected by modifying the value of the input voltage. When the input voltage X is in the high transmittance representation, the fixed ΔV decreases the luminance. As depicted in FIG. 8, the fixed ΔV makes the decreasing rate of the transmittance T(X−ΔV) greater than the increasing rate of the transmittance T(X+ΔV) (i.e., the difference between T(X−ΔV) and T(X) is greater than the difference between T(X+ΔV) and T(X)). In addition, because the highest voltage value is usually fixed, it cannot be changed by adjusting the input signal, so the overall luminance of the display may deteriorate.
Thus, it is an important subject in the display industry to provide an LCD device and driving method capable of improving the image displaying γ property of and further enhancing color difference compensation.